Thin substrate and polymer substrate LCD panels can provide mechanical characteristics such as flexibility that is similar to organic LED (OLED) displays. Such thin substrate LCDs desirably use backlights with similar mechanical characteristics.
High dynamic range LCDs (HDR-LCD) can achieve dynamic ranges that are superior to that which can be provided by an LCD optical mode alone. An array of light sources such as LEDs (light emitting diodes) that is addressed with lower resolution image data is provided in a local dimming LCD backlight, such that dark areas of an image are illuminated by the backlight with low luminance, and bright areas are illuminated with high luminance.
One type of LCD backlight comprises a light guide plate, and array of input light sources such as LEDs at one end of the light guide plate. Light that propagates by total internal reflection within the waveguide is output by means of surface features that adjust the propagation angle of light within the waveguide and allow extraction at angles close to grazing the outside of the waveguide. Such light is directed in a normal direction to the LCD by means of a turning film and/or rear reflectors. Such optical stacks may have high efficiency, but have multiple optical components with total backlight thickness typically 1 mm or greater. Such an edge illuminated light guide plate is not typically appropriate for two-dimensional local dimming for HDR-LCD illumination, or free-form shaped LCD.
Other known backlights incorporate an array of light emitting diodes (LEDs) in a matrix behind the LCD such as described in US patent application number US20170261179 comprises a plurality of spatially separated packaged LEDs and a multiple “batwing” optical elements, each batwing optical element arranged to direct light from the packaged LED in a lateral direction. Such light is strongly diffused to provide output illumination. Such backlights require expensive pick-and-place LED and individual optics alignment and have a high thickness and reduced efficiency in comparison to edge illuminated backlights.
Illumination systems for environmental lighting such as automobile headlights, architectural, commercial or domestic lighting may provide a narrow directional light output distribution, for example by means of focussing optics to provide spotlighting effects, or can achieve a wide directional light output distribution for example by means of diffusing optics.
In this specification LED refers to an unpackaged LED die chip extracted directly from a monolithic wafer, i.e. a semiconductor element. This is different from packaged LEDs which have been attached to a lead frame in order to provide electrodes and may be assembled into a plastic package to facilitate subsequent assembly. Packaged LEDs are typically of dimension greater than 1 mm, and more typically of dimension greater than 3 mm and are assembled by conventional Printed Circuit Board assembly techniques including pick and place methods. The accuracy of components placed by such assembly machines may typically be about plus or minus 30 micrometres. Such sizes and tolerances prevent application to very high resolution displays.
Micro-LEDs may be formed by array extraction methods in which multiple LEDs are removed from a monolithic wafer in parallel and may be arranged with positional tolerances that are less than 5 micrometres.
White LED lighting sources can be comprised of separate spectral bands such as red, green, blue and yellow, each created by a separate LED element. Such sources enable users to resolve the separate colours, and as a result of the separation of the sources in the lamp, can create coloured illumination patches. It would be desirable if the sources were homogenized so that their separation was less than the visual resolution limit.
Catadioptric elements combine refractive surfaces (dioptrics) and reflective surfaces (catoptrics), which may provide total internal reflection or reflection from metallised surfaces. Backlights employing catadioptric optical elements with small output luminous intensity solid angles are described in WO2010038025 incorporated by reference herein in its entirety.